Talk:Greisen-Zatsepin-Kuzmin limit

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[edit] Edits from June 2005

I've changed the phrasing of most of the text back to the version from May 9th. Mainly this was because it didn't appear to add much new information, while making the text longer and much less readable.

I've kept the notes about pion production, and will be happy to tweak the text to include additional points that any of you feel are currently glossed over in the text. However, the only other point that was added (about non-big-bang origin of the CMB) doesn't appear to actually change the situation (regardless of where the CMB came from, it should interact with high-energy cosmic rays). --Christopher Thomas 21:09, 20 Jun 2005 (UTC)

[edit] I don't understand

The paradox seems to hinge on the assumption that these very-high cosmic rays are extra-galactic in origin. Curiously the article doesn't claim this though it does say that they are 'from distant sources'. In any case is the number of observed events and their resolution good enough to suggest an extragalactic origin with high confidence? Also couldn't SNRs provide a source of these cosmic rays in the Milky Way? They certainly are one source of very-high energey gamma-rays. I'm probably missing something here and it would be great if someone could answer these points (at least the ones which aren't too obvious) in the article. --80.98.226.20 01:37, 3 January 2006 (UTC)

My understanding is that the high-energy cosmic rays are believed to be of extragalactic origin because no obvious nearby source could be found in the directions of the bursts. However, current cosmic ray observatories have a hard time detecting enough events and pinning down their directions with enough accuracy to make an ironclad case for this, so experiments are still ongoing. Even if they're of extragalactic origin, we should be able to locate the galaxies or other features that produce them. --Christopher Thomas 05:22, 3 January 2006 (UTC)

As far as I understand it, it is even so that we do not expect any source in our galaxy which produces particles at these energies, despite the directional resolution. --yanneman 11:09, 31 January 2007 (UTC)

UHECRs above the GZK cutoff could arise from either nearby or distant sources. In some theories, UHECRs could be produced nearby by the decay of hypothetical particles. At this time there are no confirmed UHECR sources. The paths of extragalactic charged particles at all but the highest energies would be bent too much by galactic and intergalactic magnetic fields to directly observe their precise origin. At the 2007 ICRC conference the Auger experiment released a spectrum confirming the observation of "a" cutoff as originally observed by the HiRes experiment. Some doubt is still expressed as to whether this steepening in the energy spectrum is caused by the GZK effect. One would expect a GZK cutoff for UHECRs of extragalactic origin. A steepening consistent with the GZK cutoff has now been observed.

[edit] Pönkle-Zedkov curves

I can't find any reference to these in the Greisen or Zatsepin and Kuzmin papers, (or anywhere else on the web), so I've removed the mention. Let me know if I'm in error. Akriasas (talk) 17:49, 13 April 2008 (UTC)